Generation High Temperature Superconducting Wire Research Articles

Three-Dimensional Numerical Study on Transport AC Loss of Soldered-Stacked-Square-Twisted (3S-T) Wire

High-temperature superconducting (HTS) soldered-stacked-square (3S) wire has been proposed as a novel potential structure for the second generation HTS wire. Twisted method is an available way to decrease the anisotropy and improve the performance of 3S wire in high field application. This paper presents a three-dimensional numerical model based on H-formulation for the 3S-twisted (3S-T) wire. AC loss is evaluated as an important parameter when 3S-T wire is applied in alternating current or magnetic field circumstances. Three different structures of 3S-T wires are considered, and the validity of the general model is verified by the corresponding experimental results. The results show that there is no significant eddy loss existing in the 3S-T wire. Moreover, if more HTS tapes are contained in 3S-T wires, the current distribution will be closer to elliptical shape and the current phase in different YBCO layers will be changed. The transport AC loss can be slightly reduced through the twisted method. The work in this paper will be helpful to understand the electromagnetic characteristics of 3S-T wire.

Analysis on Critical Current Density of an HTS Conductor With Quasi-Isotropic and High Engineering Current Density

A high-temperature superconducting (HTS) conductor with quasi-isotropic and high engineering current density is proposed. The HTS conductor consists of inner quasi-isotropic strand and outer power cable. The inner quasi-isotropic strand, equivalent to a former, is a twisted quasi-isotropic conductor made from four components stacked by the second generation (2G) HTS wire with symmetrical arrangement. The outer conductor is made by winding the 2G wire on the inner conductor that is equivalent a power cable. Simply speaking, the HTS conductor is a power cable with replacing the copper former by HTS quasi-isotropic strand so that its engineering critical current is high. The HTS conductor has quasi-isotropic critical current density, since it is a combination of a quasi-isotropic strand and an isotropic power cable. The engineering current density is improved by changing twisting pitch of inner quasi-isotropic conductor and pitch of outer power cable, the conductor is also of benefit to mechanical flexibility and quasi-isotropic critical current density. Additionally, the critical current density of inner quasi-isotropic strand is higher than the one in self-field by considering the effect of longitudinal magnetic fled taking into account.

Electrical Characteristics of Second Generation High Temperature Superconducting Wires for Power Device Application

Three kinds of second generation (2G), high temperature superconducting(HTS) wires were characterized for critical current density and over-current behavior under over-current conditions cooled by liquid nitrogen. The critical current density and over-current behavior were measured as a function of increasing temperature and current ramping rate, respectively. The critical current density of HTS wire proportionally decreased with increasing temperature. The critical temperature of the GdBCO HTS wires was higher than that of the YBCO HTS wires. An instantaneous breakdown was observed after 30A/sec of the current ramping rate. Stabilizers were delaminated after the over-current test. Over-current behavior is particularly important in HTS power device applications because the short circuit current can be much larger than the steady state value. These results are in the context of important design and fabrication considerations of HTS power devices application.

2G HTS wires made on 30 μm thick Hastelloy substrate

REBCO (RE = rare earth) based high temperature superconducting (HTS) wires are now being utilized for the development of electric and electromagnetic devices for various industrial, scientific and medical applications. In the last several years, the increasing efforts in using the so-called second generation (2G) HTS wires for some of the applications require a further increase in their engineering current density (Je). The applications are those typically related to high magnetic fields where the higher Je of a REBCO wire, in addition to its higher irreversibility fields and higher mechanical strength, is already a major advantage over other superconducting wires. An effective way to increase the Je is to decrease the total thickness of a wire, for which using a thinner substrate becomes an obvious and attractive approach. By using our IBAD-MOCVD (ion beam assisted deposition-metal organic chemical vapor deposition) technology we have successfully made 2G HTS wires using a Hastelloy® C276 substrate that is only 30 μm in thickness. By using this thinner substrate instead of the typical 50 μm thick substrate and with a same critical current (Ic), the Je of a wire can be increased by 30% to 45% depending on the copper stabilizer thickness. In this paper, we report the fabrication and characterization of the 2G HTS wires made on the 30 μm thick Hastelloy® C276 substrate. It was shown that with the optimization in the processing protocol, the surface of the thinner Hastelloy® C276 substrate can be readily electropolished to the quality needed for the deposition of the buffer stack. Same in the architecture as that on the standard 50 μm thick substrate, the buffer stack made on the 30 μm thick substrate showed an in-plane texture with a Δϕ of around 6.7° in the LaMnO3 cap layer. Low-temperature in-field transport measurement results suggest that the wires on the thinner substrate had achieved equivalent superconducting performance, most importantly the Ic, as those on the 50 μm thick substrate. It is expected the 2G HTS wires made on the 30 μm thick Hastelloy® C276 substrate, the thinnest and with the highest Je to date, will greatly benefit such applications as high field magnets and high current cables.

Hysteresis Losses Analysis in 2G HTS Cables

The Russian Scientific R&D Cable Institute is involved in many projects on R&D high-temperature superconducting (HTS) power cables including those made of modern second generation (2G) HTS wires. Evaluation of ac losses and methods for the reduction of the ac losses are important in the design of the cables. A fine experimental technique has been developed and implemented to measure ac losses in representative cable models with a length of ~5 m. However, only calculation can provide ac loss prediction in cases when it could be difficult to make measurements. Thus, we need a comprehensive simulation model to calculate ac losses. In HTS cables made of 2G wires, the main ac loss is a hysteresis loss, which only numerical simulation can predict for full-size 2G cables. We develop a finite-element method model to solve the electromagnetic problem for the calculation of ac losses. The model takes into account the strong nonlinear resistivity of the HTS materials, the hysteresis behavior of the magnetic substrate, the nonuniformity of critical current density across the tapes of the cable, and the possible ferromagnetism of a substrate. The model also takes into account any geometrical aspect of the 2G HTS cables. The details of the model and comparisons of calculations with our measurements of the ac losses are presented.

Spatial Investigation on Structural Properties of GdBa2Cu3O7 − x Coated Conductors Grown on IBAD-MgO Based Stainless-Steel Substrates

The performance of high-temperature superconducting (HTS) wires has been studied for various substrates and buffer layers. Progress is still being made to find new materials for use as superconducting layers, buffer layer, and substrates for HTS wires. Therefore, it is important to investigate the stacking structure of the commercial wires to improve their performance. Among the commercial wires, GdBCO coated conductors on stainless-steel (STS) were studied in this paper. STS can be purchased at a competitive price, and therefore it is a promising substrate for use in second generation (2G) HTS wires. To analyze structural properties of the GdBCO coated conductors on the STS substrate, several characterization tools are used. Scanning transmission electron microscopy (STEM) with energy dispersive spectroscopy (EDS) was used to investigate microstructure of films. In addition, we performed scanning laser microscopy on the conductors at room temperature to identify a map of the inhomogeneity positions. Raman scattering spectroscopy was also used to identify the secondary phases and to verify the phase formation in the films. The results of the analysis revealed the features of GdBCO coated conductors on STS for progress of HTS wires used particularly in rotating machines for high magnetic field applications.

An applicable calorimetric method for measuring AC losses of 2G HTS wire using optical FBG

We present a new calorimetric method for measuring alternative current (AC) losses of high-temperature superconducting (HTS) tapes by optical fiber Bragg grating (FBG), which is particularly well suited for the AC loss measurement of ReBCO wires, so-called the second generation (2G) HTS wires. Compared with conventional calorimetric methods, the suggested method is both free of electromagnetic disturbance, magnetic field, and fast as well as simple. Self-field AC losses are measured by the optical FBG method and the conventional lock-in-amplifier (LIA) technique, respectively. The results show that the measured AC loss is in good agreement with those measured by the electric method, thus the presented calorimetric method would be available for measuring the AC loss of 2G wire and is expected to be generalized for the measurement of AC loss or thermal performances of HTS bulk.

Progress in Production and Performance of Second Generation (2G) HTS Wire for Practical Applications

Rare earth (RE) based second generation (2G) high temperature superconducting (HTS) wire is an emerging material that has been commercially available to a wide range of energy, scientific, industrial and medical applications including high-field magnets, fault current limiters, motors and generators, transformers, and power cables. High engineering critical current density, high mechanical strength, and high irreversibility field are the major advantages of 2G HTS wires over low temperature superconducting (LTS) wires and bismuth-based first generation (1G) HTS wires. 2G HTS wires with critical current I c (77K, self-field) of 300 ~ 500 A/cm-w and piece lengths of a few hundred meters are being routinely produced. Past and ongoing demonstration projects using the 2G HTS wires suggest that the practical application of this new material is appealing, promising and challenging. Further improvement in wire performance is desired and wire price is to be reduced. In this paper, important properties of 2G wires such as uniformity, in-field Ic and electromechanical behaviors are described. Recent technology advancements in using 2G HTS wire for practical applications are discussed.

Design and manufacture of a D-shape coil-based toroid-type HTS DC reactor using 2nd generation HTS wire

This paper describes the design specifications and performance of a real toroid-type high temperature superconducting (HTS) DC reactor. The HTS DC reactor was designed using 2G HTS wires. The HTS coils of the toroid-type DC reactor magnet were made in the form of a D-shape. The target inductance of the HTS DC reactor was 400mH. The expected operating temperature was under 20K. The electromagnetic performance of the toroid-type HTS DC reactor magnet was analyzed using the finite element method program. A conduction cooling method was adopted for reactor magnet cooling. Performances of the toroid-type HTS DC reactor were analyzed through experiments conducted under the steady-state and charge conditions. The fundamental design specifications and the data obtained from this research will be applied to the design of a commercial-type HTS DC reactor.

A Review of the Ion Beam Assisted Deposition Researches towards Industrialization for the Second Generation High Temperature Superconducting Wire Fabrication

on beam assisted deposition (IBAD) is an important technique to fabricate the second generation high temperature superconducting (2G HTS) wires. Among the fabrication routes of 2G HTS long wires, IBAD route achieved the best performance in recent years. IBAD was adopted in this field in 1991 to obtain biaxially textured buffer layers, which helped to deposit high quality YBCO superconducting films on metallic substrates for the first time. Series of experimental and industrial researches on IBAD were carried out by many groups worldwide. And in the researches lasting for over two decades, the focused material for IBAD was changed from Yttria-Stabilized Zirconia (YSZ), Gd2Zr2O7 (GZO) to MgO. In this paper, the research progresses and the main achievements were briefly reviewed.

Modeling of a 22.9 kV 50 MVA superconducting power cable based on PSCAD/EMTDC for application to the Icheon substation in Korea

Two projects for high temperature superconducting (HTS) power cable have been carried out in Korea since 2001. One of them is a HTS cable project in DAPAS (Development of Advanced Power system by Applied Superconductivity technologies) program funded by the Ministry of Education, Science and Technology. In this project, LS Cable Ltd. (LSC) and Korea Electrotechnology Research Institute (KERI) jointly developed a 22.9kV, 50MVA, 3phase, 100m HTS cable using first generation (1G) HTS wire in 2006. The HTS cable system has been tested in a power test center of Korea Electric Power Corporation (KEPCO). LSC and KEPCO have been developing a 22.9kV, 50MVA, 3phase, 500m HTS cable system using second generation (2G) HTS wire since 2008, based on the technology of the DAPAS project. This project is called as GENI (Green Superconducting Electric Power Network at the Icheon Substation) project. The target of GENI project is to install and operate the HTS cable system in the Icheon substation located in near Seoul. In order to analyze the Icheon substation power system employing the HTS cable, an analysis model of the HTS cable is necessary. This paper describes the development of an analysis model for the 22.9kV, 50MVA HTS cable that will be applied to the Icheon substation in Korea.

MOD Buffer/YBCO Approach to Fabricate Low-Cost Second Generation HTS Wires

The metal organic deposition (MOD) of buffer layers on RABiTS substrates is considered a potential, low-cost approach to manufacturing high performance Second Generation (2G) high temperature superconducting (HTS) wires. The typical architecture used by American Superconductor in their 2G HTS wire consists of a Ni-W (5 at.%) substrate with a reactively sputtered Y2O3 seed layer, YSZ barrier layer and a CeO2 cap layer. This architecture supports critical currents of over 300 A/cm-width (77 K, self-field) with 0.8 mum YBCO films deposited by the TFA-MOD process. The main challenge in the development of the MOD buffers is to match or exceed the performance of the standard vacuum deposited buffer architecture. We have recently shown that the texture and properties of MOD - La2Zr2Ogamma (LZO) barrier layers can be improved by inserting a thin sputtered Y2O3 seed layer and prepared MOD deposited LZO layers followed by MOD or RF sputtered CeO2 cap layers that support MOD-YBCO films with Ic's of 200 and 255 A/cm-width, respectively. Detailed X-ray and microstructural characterizations indicated that MOD - CeO2 cap reacted completely with MOD YBCO to form BaCeOs. However, sputtered CeO2 cap/MOD YBCO interface remains clean. By further optimizing the coating conditions and reducing the heat-treatment temperatures, we have demonstrated an Ic of 336 A/cm with improved LZO layers and sputtered CeO2 cap and exceeded the performance of that of standard vacuum deposited buffers.

Design study of superconducting sextupole magnet using HTS coated conductor for neutron-focusing device

We performed a design study of sextupole magnet using high temperature superconducting (HTS) wires. The sextupole magnet is used as a focusing lens for neutron-focusing devices. A neutron-focusing device is desired to have a large aperture and a high magnetic field gradient of G, where G=2B/r2, B is the magnetic field and r is a distance from the sextupole magnet axis. Superconducting magnets offer promising prospects to meet the demands of a neutron-focusing device. Recently NbTi coils of low temperature superconducting (LTS) have been developed for a sextupole magnet with a 46.8mm aperture. The maximum magnetic field gradient G of this magnet is 9480T/m2 at 4.2K and 12,800T/m2at 1.8K.On the other hand, rapid progress on second generation HTS wire has been made in increasing the performance of critical current and in demonstrating a long length. The second generation HTS wire is referred to as coated conductor. It consists of tape-shaped base upon which a thin coating of superconductor, usually YBCO, is deposited or grown. This paper describes a design study of sextupole magnet using coated conductors.

Progress in research, development, and pre-commercial deployment of second generation HTS wires in the USA

US efforts to develop and deploy “second generation” (2G) high-temperature superconducting (HTS) wires that use the compound Y1Ba2Cu3Ox (YBCO) or other rare-earth (RE) superconducting materials are described. Wires have been demonstrated in 20 to >200-m lengths with the YBCO deposited using vapor deposition or wet chemical processes in ultra-thin layers onto textured, buffered metallic templates, which forces the grains of the RE-BCO into near perfect alignment. Critical currents for these pre-commercial wires are now within striking distance of those achieved for commercial BSSCO wires. One expected advantage of 2G wire is a 5-fold decrease in the price of wire compared with first generation wires. Another advantage of 2G wire is the intrinsic behavior of YBCO in the presence of a strong magnetic field. Enhancements in flux pinning of at least a factor of two have been demonstrated for MOCVD and MOD deposited YBCO films. US progress towards meeting the challenging goals for the year 2006, including current exceeding 300A/cm width (77K, self-field) in 100-m lengths and engineering current density exceeding 10,000A/cm2 (65K, 3-T) is reported. In addition, initial efforts toward engineering the conductor for the mechanical and electrical properties needed for strong magnetic field applications are described.

A Versatile Laboratory Electromagnet With HTS Coils

We report the development of a laboratory electromagnet utilizing high temperature superconducting (HTS) coils which is designed to generate fields in excess of 3 Tesla, but with power consumption and size significantly below that possible with copper-wound coils for an equivalent useful field volume. The components are complete and the system is currently being assembled. The electromagnet is based around a compact iron yoke with four HTS double pancake coils, employing a total of 1.6 km of first generation HTS (Bi-2223/Ag composite) wire, to generate the field across an air-gap of 50 mm. The electromagnetic design was tailored to take into account the anisotropic in-field performance of the HTS conductor, requiring a minimization of the radial field component at the coils while retaining sufficiently open access for installation of the components of a vibrating sample magnetometer with which this magnet will be used. The HTS coils are conduction cooled with a single-stage cryocooler that delivers approximately 27 W of cooling power at the design operating temperature of 35 K; HTS current leads are employed to reduce the thermal load at the coils. In the present configuration the coils are housed in a single cryostat, but the design is easily adaptable to provide for a number of specific application requirements. Contrary to the generally held view that HTS magnets are still too expensive, this project demonstrates that utilization of HTS conductor is now an attractive option in a number of application areas.

Current Sharing in Multi-Stacked HTS Solenoid Coil

The high-temperature superconducting (HTS) electric equipment using Bi-2223 wire successfully commercialized 1st generation HTS wire, has been developing by many research groups. HTS coil is one of the most important parts in HTS electric equipment. To enlarge the critical current, the operating temperature of the equipment tends to go down and number of HTS wire tends to increase. Thus, it is very important to determine the whole critical current of HTS coil for the stable operation of HTS equipment. The whole critical current of multi-stacked wire of HTS solenoid coil is not equal to the sum of the critical current of each stacked wire because of nonuniform current sharing occurs in multi-stacked HTS wires and each HTS path does not has the same critical current. In this paper, current sharing in two types of 5-stacked HTS solenoid coils, made up of 1 copper layer which is a current buffer layer of HTS coil and 4 HTS wire layers, was analyzed. One was wound with Bi-2223 wire insulated with polyimide tape and the other was wound with noninsulated Bi-2223 wire. All of the Bi-2223 wires were reinforced with stainless steel. The simulation results of current sharing in multi-stacked HTS coils coincided well with the experimental results. Based on these results, the current sharing ratio of large scale HTS coil was also expected. The copper layer acted as a good current path when all the HTS wires were quenched.